Rotary pistons pumps, in the nature of encased rotors with rotor disks at the rotor ends and vanes between those rotor disks, which vanes move radially in and out of the rotors depending upon their location within the casing, are known.
One such device is described in U.S. Pat. No. 6,554,596 of Albert and David Patterson, issued Apr. 29, 2003, in which the vane movement, in and out of the rotor, is achieved by cam surfaces within the casing, which surfaces act on both inner and outer edges of the vanes.
In applicant's co-pending U.S. patent application Ser. No. 10/680,236 entitled rotary pistons, the outward movement of the vanes is achieved by upward extensions of shoulders at the sides of each vane, which upward extensions contain pins which are seated in races continuously extending in portions of the interior side wall of the casing and positioned so that as the pins move about the races, they draw their respective vanes outwardly and inwardly.
Other known constructions of such rotary pistons require centrifugal force, through rotation of the rotor, to force the vanes outwardly. For instance, in applicant's U.S. Pat. No. 6,896,502, issued May 24, 2005, three planar vanes are seated in rotor slots formed along chords, when the cylindrical rotor is viewed in lateral cross-section, those slots being oriented so that the planes of adjacent vanes lie at 60° angles to each other.
In applicant's co-pending U.S. patent application Ser. No. 10/680,236, filed Oct. 8, 2003, outward movement and maintenance of the outward positioning of the vanes is assisted by biasing means, for example springs.
Such rotary piston pumps are constructed to move fluids at relatively high pressure. Those portions of the rotor disks as they pass in the vicinity of the pump intake port, are under significantly lower pressure than those portions which are upstream from the outlet port, which are often under significantly higher pressure. When operating under such high pressure conditions, this pressure differential may cause the rotor disks to distort, significantly affecting the efficiency of operation of the pump and reducing the usable lifespan of pump components such as the rotor disks.
It is an object of the present invention to provide a rotary piston pump that reduces the pressure differentials acting on the rotor disks. It is a further object, of one embodiment of the present invention, to provide a rotary piston pump that uses fluid pressure within the pump to assist in movement of the vanes.